The present invention relates to devices for producing circular seams on a workpiece using a sewing machine driven in a controlled manner. The present application claims the priority of Application No. P 39 02 333.8, filed in the Federal Republic of Germany on Jan. 27, 1989.
Markers in the form of marking tools which have electrically heated branding tools and pens which are displaceable against a spring are known from DE-OS 24 49 121, and are used for making collars in the production of shirts and blouses having attached collars and comprising a plurality of layers of material. The branding tools and the cartridges are lowered onto the collar, and as a result the attaching edge of the under-collar is provided with burnt-in marks and the edge of the over-collar is provided with colored marks which can be washed off. When the collar is sewn on, the marks are aligned by hand with the shoulder seams which end at the neck hole of the body part.
An automatically controlled sewing machine having a program-controlled working cycle is known from U.S. Pat. No. 4,038,931, in which a contactless proximity switch acts as a proximity sensor to produce an output signal in dependence upon irregularities in the workpiece. By way of this output signal, intervention is effected into the control program responsible for the automatic sequence of operations, which program controls the working cycles for the workpieces being sewn. In this device, irregularities in the workpiece include, for example, unintentional folds in the material, creases, and bunching. It is the aim of this device to detect unwanted faults during the sewing operation in order to prevent damage to the workpiece.